In an engine which generate power by burning a gaseous fuel, e.g. hydrogen gas, the gaseous fuel is mixed with air before being supplied to the engine. It is necessary to mix the hydrogen gas with air with a high efficiency, and, a technique to realize it is disclosed in, for example, JP 2002-81346 A. According to the technique disclosed in this Japanese patent publication, interior paths and exterior paths are circumferentially formed in an air turbo ram engine. The interior and exterior paths alternate with each other. Air compressed by a fan is blown through the respective exterior paths, and hydrogen gas is blown through the respective interior paths, whereby the air and hydrogen gas are mixed with each other. A guide vane is provided in order to forcibly direct the hydrogen gas in each interior path to flow outward, and thus the hydrogen gas flowing out in the outward direction can be mixed efficiently with the air, which is heavier in weight, blown outward from the exterior.
This arrangement, however, is for an air turbo ram engine, and, therefore, cannot be employed for engines provided with pistons, such as a reciprocating engines and rotary engines.
An object of the present invention is to provide a mixer which can mix air with a gas having a different specific gravity from air with high efficiency, and also an engine system with such mixer.